A chemical substance that cannot be broken down further using standard chemical techniques is known as:
For example, carbon (C) is an element. Atoms of a particular element always have the same number of protons. For example, all carbon atoms have 6 protons!
What is the difference between an atom, a molecule, and a compound?
An atom is the fundamental unit of matter. Atoms contain protons, neutrons, and electrons.
A molecule is a group of two or more atoms, connected by chemical bonds (for example, O2).
A compound is a molecule that contains atoms of more than one element (for example, H2O).
Which of the following are contained within the nucleus of a typical atom?
A typical atomic nucleus contains protons and neutrons. Electrons are not found in the nucleus; instead, they are located in regions (“shells”) surrounding the nucleus.
For the AP Biology exam, remember that a proton has a positive charge, while an electron has an equivalent negative charge. Neutrons are neutral, meaning that they are uncharged.
Isotopes are atoms with the same number of:
Isotopes are atoms with the same number of protons, meaning that they must represent the same element. Isotopes differ in their number of neutrons.
an ionic bond
An ionic bond is a chemical bond that forms due to the complete transfer of electrons from one atom to another.
The atom that gains electrons is given a negative charge, while the atom that gives up electrons is given a positive charge.
a covalent bond
A covalent bond is a chemical bond that forms via the sharing (not complete transfer) of electrons.
When the electrons are shared unequally, the bond is polar covalent. For example, H2O contains two polar covalent bonds between H and O, because these atoms have different electronegativities (attraction to electrons in a bond).
When the electrons are shared equally, the bond is nonpolar covalent. For example, O2 contains a nonpolar covalent bond between the two O atoms, which have the same electronegativity.
What is the chemical formula for water, and is the water molecule polar or nonpolar?
Water has a formula of H2O, and it is polar.
The water molecule (shown here) is bent due to the presence of two lone pairs on the central oxygen atom. Oxygen is more electronegative than hydrogen, so the oxygen atom will carry a partial negative charge, while the hydrogen atoms will be partially positive. Molecules with asymmetrical charge distributions like this one are polar.
How do hydrogen bonds differ from ionic or covalent bonds?
Hydrogen bonds are intermolecular, which means they occur between two or more different molecules. Ionic and covalent bonds are intramolecular, meaning they connect atoms within a single molecule.
Hydrogen bonds are attractive forces. For the AP Biology exam, be sure to remember that water molecules can hydrogen bond with each other.
a hydrophilic compound
A hydrophilic compound is one that is attracted to water.
Since water is polar, it tends to attract other polar compounds.
a hydrophobic compound
A hydrophobic compound is one that is repelled by water.
Since water is polar, it tends to repel nonpolar compounds. A classic example is an oil slick on the top of the ocean. Oil is nonpolar, so it is not attracted to the ocean water, and the two liquids do not mix.
A macromolecule is a molecule that contains an extremely large number of atoms.
For the AP Biology exam, most macromolecules you need to know are polymers, or long chains of smaller subunits.
Name the four main types of organic macromolecules that are found in living organisms.
Carbohydrates, lipids, proteins, and nucleic acids
Carbohydrates are commonly known as sugars, and lipids are commonly known as fats.
What is the general chemical formula for a typical carbohydrate?
A typical carbohydrate has a chemical formula of (CH2O)n, where n is an integer.
This can be easily remembered, since H2O represents water. Carbohydrates are simply “hydrated carbons.” Note that a few rare carbohydrates, like deoxyribose, have formulas that differ from this rule.
Define a monosaccharide and give two common examples.
A monosaccharide is a carbohydrate that contains only a single sugar subunit.
Classic examples that you should know for the AP Biology exam are glucose and fructose.
Define a disaccharide and give three common examples.
A disaccharide is a carbohydrate that consists of two sugar subunits, joined by a bond called a glycosidic linkage.
Classic examples that you should know for the AP Biology exam are maltose, lactose, and sucrose.
Define a polysaccharide and give three common examples.
A polysaccharide is a carbohydrate that consists of a polymer (or long chain) of many sugar subunits.
Classic examples that you should know for the AP Biology exam are glycogen, starch, and cellulose.
What type of reaction occurs when two carbohydrate subunits combine to form a disaccharide?
A dehydration reaction
Dehydration reactions involve the combination (or condensation) of smaller reactants to form a larger product. This occurs along with the loss of a water molecule.
What is the molecular formula for glucose?
Remember this formula for the AP Biology exam! Glucose is a six-carbon monosaccharide (meaning that it contains only one sugar subunit).
What is the molecular formula for sucrose?
Sucrose is a disaccharide, meaning that it consists of two sugar subunits. Specifically, these subunits are glucose and fructose.
The main component of plant cell walls is classified as which of the four main types of organic macromolecule?
Plant cell walls are composed of cellulose, which is a polysaccharide, or carbohydrate polymer.
Protein molecules are composed of smaller subunits known as:
Amino acids are the monomers, or individual subunits, that make up protein molecules. Adjacent amino acids are held together by peptide bonds.
Which two functional groups are found in all amino acids?
An amino acid must contain an amine and a carboxylic acid. Each amino acid also contains a specific side chain.
The amino acids that you may see on the AP Biology exam are alpha amino acids, meaning that the amine group, the side chain, and the carboxylic acid are all attached to the same central carbon.
What functional group is present in all peptide bonds?
Peptide bonds contain amides. In fact, they are sometimes alternatively known as amide linkages.
A peptide bond forms when the amine group of one amino acid attacks the carbonyl carbon of another.
A laboratory technician is analyzing the composition of a plasma protein. Which elements could he expect to find in this protein’s structure?
Carbon, hydrogen, oxygen, and nitrogen
Sulfur also may be present, depending on the particular amino acids in the structure. Some proteins also contain trace amounts of selenium.
Which would be expected to have a higher molecular weight: a dipeptide or a polypeptide?
A polypeptide would weigh more than a dipeptide.
A dipeptide is the smallest form of peptide and contains only two amino acids bound together. Polypeptides typically consist of long strings of amino acids, making them significantly heavier; a polypeptide can include up to around 50 amino acids in total.
Name the four levels of protein structure.
The four levels of protein structure are:
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
the primary structure of a protein
The primary structure of a protein is simply its linear amino acid sequence.
Primary structure is often written using either a one- or a three-letter abbreviation for each amino acid (for example, “Gly-Pro-Ile-Cys…” or “GPIC…”).
the secondary structure of a protein
The secondary structure of a protein refers to the folding of the amino acid chain into repetitive structures due to hydrogen bonding between backbone groups.
Two forms of secondary structure that you should remember for the AP Biology exam are alpha helices and beta-pleated sheets. The partial structure of a beta-pleated sheet is shown here.
the tertiary structure of a protein
The tertiary structure of a protein refers to its large-scale three-dimensional shape.
Tertiary structure is determined by interactions between side chains and by hydrophobic interactions (the tendency for nonpolar groups to avoid facing the watery environment).
the quaternary structure of a protein
Quaternary protein structure is present only in proteins that are composed of multiple subunits. This level of structure refers to interactions between subunits.
For example, hemoglobin (shown here) consists of four separate subunits, held together by various interactions and attractive forces.
Lipids are a class of organic macromolecule. Lipids are characterized by their nonpolar (non-water-soluble) nature.
Most notably, lipids include triglycerides (fats), oils, steroids, waxes, and phospholipids.
What functional groups are present in a typical fatty acid?
A fatty acid includes a carboxylic acid (COOH) group attached to a hydrocarbon chain.
Fatty acids can combine with glycerol to form triglycerides, or fat. Fatty acids can also be broken down to provide cells with energy.
What type of lipid is pictured here?
The lipid pictured here is a triglyceride, commonly known simply as a fat.
A triglyceride consists of three fatty acid molecules attached to a three-carbon glycerol backbone.
The diagram below depicts a fatty acid. Is this fatty acid saturated, monounsaturated, or polyunsaturated?
This fatty acid is polyunsaturated.
Saturated fatty acids have carbon chains that include only single bonds, while unsaturated fatty acids include one or more double bonds in their chains. Since this fatty acid contains three carbon-carbon double bonds, it is polyunsaturated. (To be monounsaturated, a fatty acid must include only one double bond in its carbon chain.)
What type of lipid would be expected to be most predominant in a eukaryotic cell membrane?
The cell membrane (in both eukaryotes and prokaryotes) is composed mainly of phospholipids in the form of a “bilayer,” or double layer.
What class of lipid is derived from the molecule below and plays a vital role in the endocrine system?
Steroid hormones are derived from cholesterol (shown here). These lipid molecules can be easily spotted due to their structures, which include four fused rings.
A typical phospholipid includes both a polar “head” region and two nonpolar “tails.” What term describes this property of having both polar and nonpolar regions?
Molecules with both polar and nonpolar regions are amphipathic.
Specifically, the polar “head” region includes phosphate, which is charged; this charge is what gives the head group its polarity. The two “tails” consist of fatty acids, which are largely nonpolar due to their long hydrocarbon chains.
Nucleic acids are a class of organic macromolecule. These molecules consist of long chains of nucleotide monomers and are involved in the storage and transmission of genetic material.
The two nucleic acids to know for the AP Biology exam are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Structures like that shown below are found in which of the four major classes of organic macromolecules?
The structure pictured here is a nucleotide, as is evident from its nitrogenous base, sugar, and phosphate group. Nucleotides are the monomers (“building blocks”) that form nucleic acids, including DNA and RNA.
A student is analyzing an unknown biomolecule. He knows that the molecule includes covalent bonds and that it is not a lipid. He is also certain that the molecule contains carbon, hydrogen, and phosphorus, although it may also include other elements. This biomolecule is most likely a:
All four of the main classes of organic macromolecule include covalent bonds, so that piece of information is unhelpful. However, only nucleic acids and (some) lipids can contain phosphorus. Since we are told that this molecule is not a lipid, it must be a nucleic acid.